This document discusses developing applications and integrating with GlusterFS. It describes using the libgfapi library to access GlusterFS volumes, providing improved speed over FUSE. The document outlines the Python and C APIs for libgfapi and provides an example of using the Python API. It also discusses rapidly prototyping GlusterFS translators using the Python Glupy library and provides a simple "hello world" translator example.

1. Developing Apps and Integrating with
GlusterFS
Justin Clift, GlusterFS Integration
Open Source and Standards team @ Red Hat
Gluster Community Day London 2013

2. #whoami
● Previously an experienced SysAdmin
(Solaris and Linux) for many, many years
● Now works on GlusterFS integration
● Mostly worked on Mission Critical
systems in corporate/enterprise
environments (eg. Telco, banking,
Insurance)
● Has been helping build Open Source
Communities after hours for many years
(PostgreSQL, OpenOffice back in the day)
● Joined Red Hat mid 2010
jclift@redhat.com

3. September 2013 - Niels de Vos
Agenda
● Options for Gluster Application development
● What is Libgfapi?
● Pros & Cons
● Libgfapi example
● Rapid Prototyping GlusterFS Translators
● Translator example
● Contact Me

4. The old way: access through FUSE

5. libgfapi: access through library

6. Pros: Why use Libgfapi?
● Improved speed and latency
● Eliminate the FUSE and kernel VFS layer from
GlusterFS volume access
● Examples:
– qemu storage layer
– Samba VFS plugin

7. Cons: Downsides
● Existing applications need to be extended
– Not a drop in replacement for POSIX based filesystem
access
● Client side API only available for C and
Python so far

8. Python and C API
● The C API is fairly comprehensive
– 87 callable C functions. Eg:
● glfs_creat()
● glfs_open()
● glfs_close()
● glfs_seekdir()
● glfs_stat()
● glfs_chmod()
● The Python API is only 19 functions so far
– Just the most used ones, more coming

9. Python API – Volume operations
● set_logging(path, level)
● mount()
● creat(path, flags, mode)
● getxattr(path, key, maxlen)
● listxattr(path)
● lstat(path)
● mkdir(path)
● open(path, flags)
● opendir(path)
● rename(old_path, new_path)
● rmdir(path)
● setxattr(path, key, value, vlen)
● unlink(path)

10. Python API – File operations
● fsync()
● read(buflen, flags)
● read_buffer(buf, flags)
● write(data, flags)
● fallocate(mode, offset, len)
● discard(offset, len)

11. Libgfapi example
Example Python code:
# Import Python libgfapi library (required)
from gluster import gfapi
# Mount the volume
vol = gfapi.Volume('f19laptop', 'playground')
vol.mount()
# Create a file
import os
myfile = vol.creat('somefile.txt', os.O_RDWR, 0o640)

12. Libgfapi example (continued)
# Write to the file
bytes_written = myfile.write('This is some data')
print bytes_written
# Seek back to the start of the file
myfile.seek(0, os.SEEK_SET)
# Read from the file
file_data = myfile.read(5)
print file_data
# Rename the file
vol.rename('somefile.txt', 'someotherfile.txt')
# Delete the file
vol.unlink('someotherfile.txt')

13. Rapid Prototyping GlusterFS
Translators
● Uses the Python Gluster “Glupy” library
● Easy to write translators, compared to C
● Not as fast to execute as C based translators, but can
still fire off over 1,000 times per second

14. Trivial “helloworld” example
import sys
from gluster_glupy import *
class xlator (Translator):
def __init__(self, c_this):
Translator.__init__(self, c_this)
def lookup_fop(self, frame, this, loc, xdata):
print "Python xlator: Hello!"
dl.wind_lookup(frame, POINTER(xlator_t)(), loc, xdata)
return 0
def lookup_cbk(self, frame, cookie, this, op_ret, op_errno, inode, buf, xdata, postparent):
print "Python xlator: Hello again!"
dl.unwind_lookup(frame, cookie, this, op_ret, op_errno, inode, buf, xdata, postparent)
return 0

15. Helloworld translator demo
[Run through the helloworld demo here]

16. Real world example
● GlusterFlow translator:
https://forge.gluster.org/glusterflow/glusterflow/blobs/master/json/glus
terflowclient.py
● Fires off 1,600 times per second on my laptop in a F19 VM
● Can be re-written in C if that's not fast enough

17. Questions?
● User questions and experiences
– gluster-users@gluster.org
– #gluster on Freenode IRC
● Developer questions and discussions
– gluster-devel@nongnu.org
– #gluster-dev on Freenode IRC
● Announcements mailing list
– announce@gluster.org

18. Contact me
● Happy for people to email me about any of this
stuff:
Justin Clift
● Work email: jclift@redhat.com
● Personal email: justin@postgresql.org
● Twitter: @realjustinclift